The overall objective this project is to ascertain the relationship between mitochondrial mutations and aging. Mutations are known to accumulate in the mitochondrial genome with age, concomittantly with a decline in mitochondrial function. However, we lack direct evidence for a causal role of mitochondrial mutations in longevity and age-associated pathology. According to current information, DNA polymerase gamma (pol gamma) is the sole DNA polymerase responsible for replication and repair of the mitochondrial genome. Hence it is probable that errors made by pol gamma during copying of mitochondrial DNA are a major source of mitochondrial mutations; this possibility is especially relevant in view of the high levels of oxidative damage in mitochondria, and the lack of nucleotide excision repair and mismatch repair. This project will employ biochemical approaches and mouse models to address the relationships of pol gamma fidelity, mitochondrial mutations, and longevity. In specific aim I we will measure the accuracy of pol gamma in copying past oxidative lesions that are known to be mutagenic. In specific aims 2 and 3, we will create transgenic ("knock-in") mice that harbor mutator or anti-mutator alleles of pol gamma, and measure the effects of allele replacement on mitochondrial mutations, age-associated phenotypes and life-span. In specific aim 4, we will utilize a mouse model to assess the interaction of pol gamma with oxidative damage by analyzing the effect of anti-mutator pol gamma in an "MCAT" mouse that overexpresses catalase in mitochondria. The MCAT mouse has recently been shown to exhibit a 20% extension in lifespan. It is possible that increased accuracy of mitochondrial DNA replication, combined with reduced levels of oxidative DNA damage, will produce a lower frequency of mutation and a greater extension of lifespan than observed in either anti-mutator or MCAT mice.